Stepwise enrichment of 15N along food chains: Further evidence and the relation between δ15N and animal age

Identifying nutrient sources to three lagoons at Ofu and Olosega, American Samoa using δ15N of benthic macroalgae

“…The nitrogen content (percent total nitrogen, concentration of the heavier nitrogen isotope 15 N, and d 15 N values) of macroalgae varies by species (due to physiology and biochemical processes), light regime, temperature, and availability of nitrogen and 15 N content of the water (e.g., Heikoop et al, 1998;Cohen and Fong, 2006). Values of d 15 N in this study (Table 3) were close to or lower than those reported for oligotrophic suspended particulate matter (4-5&; Waser et al, 2000), pelagic and coastal marine seaweeds (5-8& in Minagawa and Wada, 1984), and the euphotic layer DIN (7-10&; Minagawa and Wada, 1986). The low d 15 N values of the macroalgae, the low nutrient concentrations of lagoon waters, the lack of correlation between d 15 N values and distance from shore, and the low concentrations of nutrients in well-water samples indicate that the major sources of nutrients to the three Ofu-Olosega lagoons at the time of this study were most likely oceanic/atmospheric, and not animal/anthropogenic in origin.…”

“…Biological processes usually result in fractionation of the isotopes of elements (such as nitrogen and carbon) incorporated by organisms and plants (Minagawa and Wada, 1984). The ratio of 15 N to 14 N {more specifically the d 15 N (&) = [( 15 N/ 14 N sample)/ ( 15 N/ 14 N atmospheric nitrogen) À 1] · 1000} in tissue has been reported to be effective in distinguishing between sources of nitrogen (e.g., atmospheric deposition, fertilizer, nitrogen fixation, and animals or plants; Peterson and Fry, 1987) and trophic level (the higher the trophic level, the greater the d 15 N; e.g., Minagawa and Wada, 1984). Atmospheric deposition and fertilizers have relatively low d 15 N values (À12& to +5& and À3& to +3&, respectively;Kreitler and Browning, 1983;Russell et al, 1998).…”

Geographic Information System-Based Source Estimation of Copper Pollution in Lake Itezhi-tezhi and Metal-Accumulation Profiles in Oreochromis spp. from Both Field and Laboratory Studies

“…The highest difference we found was 4.71‰ between Serranochromis sp. and Labeo cylindricus, indicating an increase in trophic level (Minagawa and Wada, 1984).…”

“…After each sample was weighed out into a tin capsule, stable isotope ratio was determined using an isotope ratio mass spectrometer equipped with an elemental analyzer (Fisons NA1500-Finnigan MAT 252). Stable isotope ratios were expressed in δ notation, as the deviation from standards in parts per thousand (‰), according to the following formula: δX = [(R sample /R standard − 1)] × 1000, where X is 13 C or 15 N and R is the corresponding ratio 13 C/ 12 C or 15 N/ 14 N (Minagawa and Wada, 1984). Data are presented as the values based on the international standard of v-PDB (Vienna Peedee Belemite) and atmospheric N 2 for C and N, respectively (Minagawa and Wada, 1984).…”

“…Stable isotope ratio analysis has increasingly been used to assess the relationship between trophic levels and accumulation levels of environmental pollutants in an ecosystem (Revenga et al, 2011). Moreover, stable carbon isotope ratios (δ 13 C) have been used to evaluate dietary sources within a freshwater food web (Peterson and Fry, 1987), whereas nitrogen isotope ratios (δ 15 N) are reported to increase 2-4‰ (average: 3.4‰) with increasing trophic levels (Minagawa and Wada, 1984). In our field study, we focused on Cu as we noted above that the Lake ITT could be contaminated with Cu.…”